N4329R

On July 8, 2018, about 0643 eastern daylight time, a Best Off Skyranger experimental light-sport airplane, N4329R, was substantially damaged when it was involved in an accident at Houghton Lake State Airport (5Y2), Houghton Lake, Michigan. The pilot sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, he did not observe any anomalies with the airplane or its engine during the preflight inspection or the before-takeoff engine run-up. The fuel tank contained about 12 gallons of automotive fuel before the flight. The pilot reported that the takeoff roll, rotation, and initial climb from runway 16 were uneventful; however, as the airplane climbed through 150 ft above ground level, the engine speed rapidly decreased from 6,200 rpm to 4,700 rpm. He verified that the throttle was full forward, the ignition switch was selected to both, the fuel valve was open, and that available fuel was in the tank. The pilot also turned on the electric fuel pump. Despite the pilot's corrective actions, the engine continued to operate at a decreased power setting, and the airplane was unable to maintain altitude. The pilot reported that there were trees ahead of the airplane's flightpath, so he made a turn into the wind and maneuvered to land on a nearby golf course fairway. The pilot stated that the airplane had insufficient altitude and airspeed to flare normally, which resulted in a hard landing on the fairway.

A postaccident wreckage examination was completed by a Federal Aviation Administration (FAA) airworthiness inspector. The FAA inspector reported that both wings and the empennage sustained substantial damage during the forced landing. The Rotax 582 engine did not exhibit any crankcase or cylinder fractures, and there were no oil/fluid leaks observed on the exterior engine components. The firewall-mounted oil reservoir contained ample engine oil. The three-blade propeller remained attached to the engine and exhibited blade damage consistent with rotation at impact. Two spark plugs, one from each cylinder, were removed and exhibited normal wear signatures. The remaining two spark plugs were damaged during the accident and were not removed.

Both carburetors had separated from their respective induction tubes during impact; however, both carburetor throttle arms remained attached to the control cable that was continuous to the cockpit throttle. A partial disassembly of both carburetors revealed ample automotive fuel in their respective bowls. No contamination was observed in the carburetor bowls or the fuel screens. The FAA inspector rotated the propeller by hand and confirmed mechanical continuity of the internal drivetrain components of the engine. The dual electronic ignition system appeared undamaged and was not tested. The postaccident examination did not reveal any evidence of a mechanical malfunction that would have precluded normal engine operation during the flight.

According to a carburetor icing probability chart contained in FAA Special Airworthiness Information Bulletin CE-09-35, entitled "Carburetor Icing Prevention", the recorded temperature and dew point were in the range of susceptibility for the formation of carburetor icing. The bulletin notes that if ice forms in the carburetor of a fixed-pitch propeller aircraft, the restriction to the induction airflow will result in roughness in engine operation and a drop in engine speed.

The airplane was not equipped with a carburetor heat system; however, the engine was equipped two variable-venturi sliding carburetors (e.g. sliding carburetors) that are generally not prone to carburetor icing, according to Aircraft Powerplants, Fifth Edition by Bent/McKinley.